1. Field of the Invention
This invention is in the field of tubular products and bodies, and specifically to a unique tubular product, and method and apparatus for manufacturing such tubular products.
2. Description of the Related Art
The history and background of making tubes and pipes is fairly well known and will not be addressed in any detail herein. It is sufficient for the purposes of this application to simply state that since the first log and clay pipes, technology has made substantial advances.
Relatively recently in history roll-forming methods have been used to manufacture pipes and tubes from flat sheets of metal. In its most fundamental form, roll-forming imparts a radius to the flat metal stock as it is passed a plurality of times through one or more rollers. The rollers, referred to as roller dies, are precision made for each job. Each roller die is referred to as a station. As the sheet metal passes through each station, each roller changes the profile of the metal. The successive rolling through the roller dies allows for profiles that are substantially closed or open. These profiles have enormous application in manufacturing, commercial building, aerospace and other applications. Parts can be fabricated from aluminum through 6 gauge steel (½″ thick).
Additional operations may “pre-punch” holes in precise locations for mounting holes or to reduce weight of the final shape. “Notching” is another operation that may either punch through or punch part of the metal out from the surface. Shapes may be cut to precise length after “roll forming” is completed. When precision is preferred along the seam, roll forming is not an acceptable solution. Moreover, roll forming is unable to produce complex asymmetric profiles. For complex asymmetric profiles other techniques are used.
To produce a complex asymmetric tubular form or profile, extruded aluminum tubes are typically used. The aluminum may be easily formed, bent, or manipulated to produce the desired shape, but not often where all steps are performed in a single manufacturing process. Rather the aluminum tubular product is manufactured at one location, than transferred to another manufacturer who imparts the desired shape or profile to the tubular material.
Hydro-forming is one method often used to produce complex asymmetric tubular shapes. The metal tube may be filled with a liquid, sealed, and inserted into a mold. The liquid-filled tube is compressed within the mold cavity. As pressure is applied the liquid within the tube forces the walls of the tube to deform and conform to the shape of the mold cavity. Alternatively, a high pressure liquid may be introduced into the tube at the same time as external pressure is applied by the press. In the same manner as briefly described above, as the pressure increases, the metal is deformed to the areas of least resistance, forming the tube to the shape of the mold cavity.
Another method of making complex tubular products is casting. Green sane molds may contain a core set-off from the mold cavity by spacers. The molten metal is poured into the mold and allowed to cool. The green sand mold and core are destroyed to remove the finished product.
Yet another method for making complex tubular work pieces is by machining. The advent of computer aided machines now makes the formation of complex shapes rather straight forward. Virtually any complex solid may be machined from one or more billets of material. However, when it comes to machining tubular products, the results are limited especially when the tubular passages are not straight. To the writer's knowledge, no machining technique has yet been designed that can bore curvilinear or serpentine passages through metallic bodies.
U.S. Patent documents discussing the formation of tubular products by roll forming, hydro-forming, and other techniques include 6,920,772; 6,904,677; 6,892,559; 6,591,648; and 4,991,419, the contents of which are incorporated herein by reference.
A disadvantage often associated with making tubular objects using the roll-forming method is that the tubes are often not closed structures. That is to say that a substantial gap is nearly always present formed between the opposing edges of the metal sheet. Hydro-forming and casting methods are often too expensive to justify for many components. Lastly, machining has its own disadvantages limited by access to the interior of structures. As a result, none of the prior known methods are appropriate for manufacturing inexpensive arcuate or serpentine tubular work pieces where precision is important.
The invention described herein solves the disadvantages associated with the prior art by providing a method and apparatus for forming flat stock metal into tubular bodies such as axles, tubular frames, handles, or substantially any rod-like structure previously made from solid stock. The instant invention also achieves these goals with less waste and less expensive raw material than prior methods.